1. Field of the Invention
The present invention is directed to a process for producing purified solutions of blocked polyhydroxystyrene resins or purified solutions of blocked, crosslinked polyhydroxystyrene resins. These purified solutions are useful in making chemical amplified photoresist formulations.
2. Brief Description of the Art
Polyhydroxystyrene resins where some or all of the hydroxy groups in the resin are converted into acid-labile protecting groups ("blocked resins") are commonly used as polymeric materials in chemically amplified photoresists. These chemically amplified photoresists are employed in advanced photolithographic processes of semiconductor fabrication.
Crosslinked polyhydroxystyrene resins having some or all of the hydroxy groups converted to acid-labile protecting groups and also possessing crosslinking moieties ("blocked, crosslinked polymers") are also well known. See, for example, European Published Patent Application Nos. 0718316 A2, published on Jun. 26, 1996, and 0738744 A2, published on Oct. 23, 1997. Both of these published European Patent Applications are incorporated herein by reference in their entireties. These blocked, crosslinked polyhydroxystyrene resins are employed instead of or in conjunction with blocked resins as the polymeric materials in chemical amplified photoresists.
In making these blocked resins or these blocked, crosslinked polyhydroxystyrene resins, the precursors (e.g., the polyhydroxystyrene, the protecting group precursor and, optionally, the crosslinking agent) have been reacted together in the presence of an acid catalyst and suitable organic reaction solvent to form an impure solution of the blocked polymer or the blocked, crosslinked polymer in the reaction solvent. After the reaction was complete, the reaction mixture was then passed through a bed of strong base ion exchange resin to remove the acid catalyst. The treated reaction solution was then combined with deionized water or a mixture of deionized water and an alcohol (e.g., ethanol or isopropanol) to precipitate the blocked resin or blocked, crosslinked resin in solid form. The precipitated solid resin was then separated from the reaction mixture, preferably by filtration or centrifugation. The separated resin was then washed with more deionized water and then vacuum dried. The dried, solid blocked resin or blocked, crosslinked resin was later dissolved in a suitable organic photoresist solvent and then used to make a chemical amplified photoresist formulation.
This prior art method of making these blocked resins and blocked, crosslinked resins has several disadvantages associated with it, including:
(1) The resin bed employed to remove the acid catalyst must have a very low trace metals content. This need can be met by only either using a high purity and expensive ion exchange resin or using a special cleanup procedure for standard ion exchange resins after each run. Furthermore, the ion exchange resin bed must be very dry (i.e., contain no water therein) when the reaction mixture is passed through it. Otherwise, the water (in the presence of the catalyst or ion exchange resin) may hydrolyze the blocked polymer. Still further, in some cases, the ion exchange resin may act as a catalyst for unwanted reactions or may retain some of the blocked polymer or blocked, crosslinked polymer, thereby reducing the yield of the blocked polymer or blocked, crosslinked polymer. And, in any case, the employment of the ion exchange resin also requires cleanup and disposal. PA1 (2) The phase change precipitation step requires a large amount of water (i.e., at least 20 times the weight of the reaction mixture). The use of smaller amounts of water will result in sticky solids that adhere to the sides of the precipitation vessel. The large amount of water results in a large quantity of wastewater that must be disposed of. Also, a large and costly precipitation vessel must be employed. PA1 (3) The separation step requires special and costly filtration and centrifugation equipment. Handling these solids during and after this separation step is a potential source of contamination because it is almost impossible to keep these solids isolated from the environment. PA1 (4) The drying of the solids is another potential source of contamination, both from the dryer equipment itself and the handling required to load and unload the dryer. Also, drying may cause unwanted side reactions in the product to occur. PA1 (1) forming an impure reaction solution comprising blocked polyhydroxystyrene resin and acidic catalyst in reaction/photoresist solvent; PA1 (2) adding amine, at least one hydrophilic solvent, at least one hydrophobic solvent and water to said impure reaction solution, thereby forming an aqueous phase comprising water, the hydrophilic solvent and at least one salt of the amine and the acidic catalyst and an organic phase comprising the hydrophilic solvent, the hydrophobic solvent, reaction/photoresist solvent and the blocked polyhydroxy-styrene resin; PA1 (3) separating the aqueous phase from the organic phase; and PA1 (4) removing the hydrophilic solvent and the hydrophobic solvent from the separated organic phase, thereby forming a purified solution of blocked polyhydroxystyrene resin in the reaction/photoresist solvent.
Accordingly, there is a need for an improved process for preparing pure blocked resins or pure blocked, crosslinked resins without the above disadvantages of the prior art. The present invention offers such a process. In particular, the process of the present invention reduces waste generation, reduces the probability of product contamination and eliminates solids handling. This process allows for the purified resin to be directly dissolved in the photoresist solvent rather than having this purified resin put in solid form and then redissolved in the photoresist solvent.